DES MOINES, Iowa — A South Dakota company announced it will build the first commercial scale cellulosic ethanol plant in the United States, meaning it will use corn stalks and leaves — not just the kernels — to produce the renewable fuel.

With an investment of about $200 million, Broin Companies plans to expand the capacity of an existing 50 million gallon plant in Emmetsburg by an additional 75 million gallons, the company’s CEO Jeff Broin said Monday.

“Broin made a very important first step today,” said Matt Hartwig, a spokesman for the Renewable Fuels Association. “Other companies are looking at it as well, but it is a very important step for the industry as a whole.”

Abengoa Bioenergy, a company based in Sevilla, Spain, is building a cellulosic ethanol plant in Spain and is planning a pilot project in the United States. Iogen Corp., of Ottawa, Canada, produces cellulose ethanol from wheat, oat and barley straw in a demonstration facility and also is exploring a U.S. plant.

That said, most ethanol in the United States is made solely from the starch contained in a corn kernel. In this less expensive process, the starch is broken down into basic sugar components, which are fermented using yeast and a cooking process into grain alcohol.

The Sioux Falls, S.D., company, which owns 18 ethanol plants in five states, will use technology it has developed with Denmark-based Novozymes and Delaware-based DuPont that breaks down the cellulose in corn stalks and other plant parts into basic sugars that can be fermented into ethanol.

Professor Robert Brown, director of the Iowa State University Office of Biorenewables Programs, said using plant fibers to make ethanol is more difficult and costly because it takes a more sophisticated cocktail of enzymes to extract the sugars. But he said a process for converting other plant material into ethanol is a needed breakthrough to significantly expand production in the United States.

Finding a way to use materials such as perennial grasses, rapidly growing trees and corn plants can mean that the nation eventually replaces as much as two-thirds of its foreign oil demand with a homegrown fuel source, he said.

The process to be used at the Emmetsburg plant will enable the plant to make 11 percent more ethanol from a bushel of corn and 27 percent more from an acre of corn, Broin said. The process cuts the need for fossil fuel power at the plant by 83 percent by using some of its own byproduct for power, Broin said.

Most ethanol plants rely on natural gas to power their processing equipment.

Brown said many experts believe corn can be used to displace up to 12 percent of the nation’s fuel supply, but beyond that, another source for the ethanol needs to be found.

Currently, about 3 percent of the nation’s 140 billion gallon annual fuel consumption is ethanol, according to the American Coalition for Ethanol, a trade group.